This invention pertains to photographic elements, and in particular to photographic elements incorporating blocked photographic developers in a novel arrangement of layers.
It is well known in the art that the introduction of conventional color developers, such as p-aminophenols, into sensitized photographic elements containing silver halide salts, leads to desensitization of the silver halide emulsion and enhanced fog in such layers. Much effort has therefore been directed at trying to produce effective blocked developers, which can be introduced in silver halide emulsion elements without deleterious desensitization or fog effects and which unblock chemically under conditions of development so that developer is free to produce a normal silver image and/or participate in color forming (dye forming) reactions.
U.S. Pat. No. 3,342,599, to Reeves, discloses the use of Schiff base developer precursors. Schleigh and Faul, in a Research Disclosure (129 (1975) pp. 27-30), described the quaternary blocking of color developer and the acetamido blocking of p-phenylenediamines. Subsequently, U.S. Pat. No. 4,157,915, to Hamaoka et al., and U.S. Pat. No. 4,060,418, to Waxman and Mourning, describe the preparation and use of carbamat blocked p-phenylenediamines.
All of these approaches and inventions have failed in practical product applications because of one or more of the following problems desensitization of sensitized silver halide; unacceptably slow unblocking kinetics; instability of blocked developer yielding increased fog and/or decreased Dmax after storage.
Recent developments in blocking and switching chemistry have led to blocked p-phenylenediamines that perform well. In particular, compounds having ".beta.-ketoester" type blocking groups (strictly, .beta.-ketoacyl blocking groups) are described in U.S. Pat. No. 5,019,492. With the advent of the .beta.-ketoester blocking chemistry, it has become possible to incorporate developers in film systems in a form from which they only become active when required for development.
The incorporation of these blocked developers in photographic elements is carried out using colloidal gelatin dispersions of the blocked developers. These dispersions can be prepared using any means well known in the art. For example, in one such method, the developer precursor is dissolved in a high vapor pressure organic solvent (for example, ethyl acetate), along with, in some cases, a low vapor pressure organic solvent (such as dibutylphthalate), and then emulsified with an aqueous surfactant and gelatin solution. After emulsification, usually done with a colloid mill, the high vapor pressure organic solvent is removed by evaporation or by washing, as is well known in the art. The .beta.-ketoacyl blocked developers are released from the film layers in which they are incorporated by an alkaline developing solution containing a dinucleophile, for example hydroxylamine.
It has been known to the photographic art to coat a developer on the backs of plates, films and papers. In an early British Patent Specification (No. 1,201), Backelandt in 1888 disclosed the preparation of photographic plates, whereby the backs of the plates were entirely covered with a mixture comprising gallic acid or other reducing substance, salicylic acid, gum arabic, dextran, gelatin or other binder, alcohol, and water. After exposure, said plates were developed by dipping them into an aqueous ammonia solution or into a plain water solution (when half of the back of the plate had been coated with alkali in a suitable binder and when the other half of the back of the plate had been coated with the developing agents as described above). This reference showed how to incorporate sufficient developer in order to eliminate developer from the processing solution. The use of such plates, however, occasioned numerous difficulties arising from contact between the back side of one plate and the emulsion-bearing, light sensitive side of an adjacent plate in, for example, a magazine. These difficulties include mechanical scratching of one or both of the contacting layers, the desensitization of the contacted emulsion-bearing light sensitive layer by reducing agent diffusing from the adjacent incorporated developer layer, as well as difficulties from the thermal instability of the incorporated developer.
Thornton and Rothwell, in British Patent Specification No. 17,292 (April 1900), disclosed that fixing agents may in addition and in combination with developing agents be affixed to the back sides of photographic plates so that development and fixing may be done by placing the plate in a single water solution, after which the plate may be removed in daylight and subsequently washed free of residual chemicals.
In U.S. Pat. No. 786,535 (1905), Thornton and Rothwell disclosed preparation of similar back-coated plates and films, with the application of a further protective layer to the back side so as to overcome the foregoing deleterious effects of mechanical abrasion between adjacent plates, and further, to prevent oxygen from reaching the incorporated developer. Thornton and Rothwell, in U.S. Pat. No. 786,536 (1905), disclose a similar system applied to photographic paper used for producing prints from negatives.
Kelly, in British Patent Specification No. 13,835 (1907), and Bentham and Kelly, in British Patent Specification No. 26,066 (1905), disclosed the coating of a developing mixture comprised of metol (N-methyl-4aminophenol sulfate) and hydroquinone, in association with suitable borate-related compounds for pH control, to the back sides of plates, films, and printing-out papers. Development of the disclosed plates, films, and papers was obtained by placing them into a plain water solution, the required developer being acquired from that coated on the reverse sides.
Bolas, in British Patent Specification No. 24,667 (May 1907), disclosed the interposition of a neutral or inert or slightly acid preparation or sheet between the alkaline accelerator and the reducing agent.
Various automatic film processors adapted to develop, fix, wash, and dry sheets of light-sensitive material are known to those skilled in the art. Many forms of developer replenishment systems, manual and automatic, are known. For example, U.S. Pat. No. 3,386,472 describes the maintenance of a developer solution at a predetermined level of activity by delivering replenishment solution under the control of an electromechanical system.
Street et al., in U.S. Pat. Nos. 3,554,109 and 3,559,555, disclosed an image monitoring and control system for feeding replenishment chemicals to the film processor. The Street system is designed for use with sheets of image-bearing photosensitive materials.
Takita, in British Patent Specification No. 1,469,004 and in U.S. Pat. No. 3,990,088, respectively, disclosed a method for stabilizing developer activity in an automatic film processor. The disclosed method is designed to keep developer activity within certain prescribed control limits, and represents an improvement over the control process described by Street et al.
Matsugo, in U.S. Pat. No. 4,198,151, disclosed a developer replenishment system for developing photographic films. The system comprises means for automatically pumping developer replenishment solution from a reservoir to the development tank, in proportion to the width and length of film processed in the tank.
Mertz, in U.S. Pat. No. 4,046,571, disclosed a replenisher for use with a photographic developer bath. Said replenisher comprises a mixture of a 1-phenyl-3-pyrazolidone and a hydroquinone (or derivative thereof), bromide, speed restrainer, and buffer to provide a pH of 10 at 25.degree. C.
Wernicke and Meckl, in U.S. Pat. No. 4,348,475, disclosed a process based on the regenerability of the developer.
Despite the technical sophistication of automatic developer solution replenishment systems, such systems continue to be susceptible to inaccuracy in development. For example, the known systems can exhibit a tendency to over-develop images for a short time immediately after addition of replenishment solution. Such systems also show gradual loss of activity during the time in which the developer solution is sitting idle and subject to aerial oxidation.
In conventional processors, replenishing developer solution is supplied directly to the developing tank, resulting in an instantaneous surge in developing activity, followed thereafter by a decrease in activity. This cyclical variation can result in uneven developed densities.
Whatever automated replenishment system is employed, extant processors require operators to mix and load developer solutions manually into replenisher tanks, thereby exposing the operators to the possibility of physically contacting the developer solutions. Such contact, in general, should be avoided.
When developers, developer precursors, and blocked developers are incorporated in emulsion layers containing silver halide or in layers in reactive association with silver halide, said developers can cause deleterious desensitization effects and unwanted incubation fog formation upon storage, prior to development.
Elements and processes involving the coating of unblocked developers, such as hydroquinone, on the back sides of films, plates, and papers suffer in that such developers are not stable with respect to oxidation during storage.
There has been a need for a photographic element incorporating a blocked developer which is stable until development. Then the element can be developed rapidly and easily. There has also been a need for a process for developing an image in a photographic element which employs a developing solution having a simplified composition.
There has also been a need for a process for developing an image in photographic elements by means of an automated apparatus whereby the activity of the developer in the developer bath is maintained constant by automated replenishment means. There has further been a need for a process which obviates the deleterious desensitization effects and unwanted incubation fog formation upon storage of the known systems. In addition, there has been a need for a process which avoids exposure of operators to potentially harmful developer solutions.